If only these two had been BFFs! Robert Downey Jr. is hitting the talk show circuit to promote Due Date and last night David Letterman asked him about Charlie Sheen. "We were in high school together," said RDJ. "We didn’t really hang out. I mean, it sounds like we could have really partied."

And does Downey have any words of wisdom for the fellow actor? "He's a grown man, what am I gonna say? The only advice I would give him is, you know, don't get arrested."

Watch the vid above!